Glaucoma is a relatively common ocular disorder in animals. For example, glaucoma has long been recognized as a leading cause of human and canine blindness. The incidence of canine glaucoma, for example, is 0.5%. Increased incidence however is noted in specific breeds. Despite its importance, the long-term control of canine primary glaucoma, whether medical or surgical, continues to elude the veterinary profession.
The current state of the art for long term control of glaucoma in humans and/or dogs and/or other animals (hereinafter, for convenience, sometimes collectively referred to as “animals”) includes medical management, cyclophotocoagulation and anterior chamber shunts. For example, anterior chamber implants are used to drain or divert fluids, such as aqueous humor. One of the disadvantages of the art is that implants in dogs fail to maintain normotensive intraocular pressures for more than 6 months postoperatively or do so only when combined with other forms of glaucoma therapy including medical and surgical management. Some implantable glaucoma shunts are simply cylinders that are inserted nearly perpendicularly into the animal's eye and are held by frictional fit by eye tissue. In other words, one of the problems with the art is that the implantable shunts do not remain secure to the site for the purpose of draining or diverting aqueous humor extraocularly. Furthermore, postoperative hypotony occurs when aqueous humor production does not keep pace with outflow. Thus, it is imperative that outflow of aqueous humor be regulated.
Other methods of draining or diverting aqueous humor in dogs have focused on varying implants from valved to nonvalved, and altering explant sites from sclera, subcutaneous, or microvascular, to achieve a route for aqueous drainage.
Studies in humans and dogs indicate that the failure of standard drainage procedures arises mainly due to fibrosis at the site of the filtration bleb and reduced absorptive area for aqueous humor from the scarring, or tube occlusion. Cytokines including fibroblastic growth factor and transforming growth factors β1 and β2 have been demonstrated in the aqueous humor of dogs and humans with chronic ocular disease including primary glaucoma. These agents have marked mitogenic activity for mesenchymal cells which are responsible for occlusion of these filtering sites. Blocking the effects of these fibroblast stimulating cytokines may inhibit scarring and prevent failure of these filtering procedures. Numerous drugs including mitomycin-C, an antineoplastic, antibiotic agent that reduces collagen production by fibroblasts, have been used to help prevent implant obstruction. Mitomycin-C has yielded some benefit in the success rates of filtration surgeries in humans, monkeys, and rabbits, and has been noted to suppress but not prevent fibrosis around anterior chamber silicone implants in clinically normal dogs.
Many inflammatory diseases are associated with excessive or inappropriate cytokine activity. Cytokines activate lymphocytes and macrophages resulting in a markedly increased production of proteolytic enzymes which rather contribute to the inflammatory process and fibrosis. Intravascular shunting of cytokine-laden aqueous humor may suppress processes and prevent implant fibrosis. Unfortunately implant obstructions, caused by blood reflux, occurred both intraocularly and at the intravascular implant junction. These failures in conjunction with the inability of antineoplastics to prevent fibrosis around implants in dogs attest to the need of shunting aqueous humor to an epithelium-lined site with minimal exposure of mesenchymal tissue. The frontal sinus is an accessible epithelium-lined space and is a potential site for long-term extraorbital diversion of aqueous humor.
Consequently, a need exists in the art for a device and a method for the treatment of glaucoma in animals. A need also exists in the art for draining or diverting aqueous humor extraocularly.
In contrast to the prior art, the present invention provides for a shunt to drain or divert fluids, such as aqueous humor, extraocularly, from the anterior chamber to the frontal sinus via a valve with consistent opening and closing pressures, and to improve frontal sinus implantation and retention via an anchoring bulb and plug stopper.